1. Field of the Invention
This invention relates to a method of producing an article of manufacture such as channels in a heat exchanger for use in engine combustors, heat sinks and the like.
2. Description of Related Art
U.S. Pat. No. 4,707,225 describes corrosion-resistant cooling channel construction by controlled electro-deposition of select materials onto a wall substrate of a combustion chamber. In the formation of the cooling channel construction, open channels are filled with a meltable substance such as a wax composition having a melting point of from about 90.degree. C. to about 97.degree. C. During this process, the meltable substance is removed by heating followed by final preparation of the cooling channel construction.
U.S. Pat. No. 4,676,876 describes a method for the manufacture of components such as heat exchangers. In this process, a cooling canal provided in a base structure is filled with an electrically conducting filler comprising a flexible and elastically stretchable profiled rope. Following preliminary component manufacturing steps, the rope is pulled out of the formed cooling canal defining a cooling channel in the manufactured component.
U.S. Pat. No. 4,582,678 describes a method for producing rocket combustors having a cooling wall of channel construction. In this method, a filler material useful in the manufacturing process comprises a meltable metal the removal of which is caused by heating it to temperatures in the range of 100.degree. C. to 250.degree. C. The utilization of the metal filler is limited, however, by its hardness and wetability with respect to a copper on the surface of the grooves forming the cooling section of the channel construction.
In the case of methods formally used which utilized a wax or the like as the filler, a drawback has been recognized in that during molding of the final article, the wax is often deformed resulting in inconsistent cooling channels being formed in the channel construction.
Further, the aforesaid metallic filler has additional drawbacks in that the removal of the metallic filler is often incomplete requiring additional machining of the channel components; said mechanical removal thereof proving very difficult and often occasioning imperfections in the channel construction leading to impaired cooling characteristics and possible breakdown during operation of the cooling element.
However, there remains a need for a high temperature dissolvable filler material that can be used for producing heat exchangers by plasma spraying. For example, the above filler materials can be used for electroform channel closeouts which are fabricated at or near ambient temperature. Electroforming is however limited mainly to pure metals and certain binary alloys such as electroformed Ni--Co. On the other hand most structural alloys cannot be electro-deposited. This includes the highly versatile NARloy-Z (or Cu-3w/oAg-0.5w/oZr) used for construction of rocket engine combustors and the iron and nickel base superalloys employed extensively in jet and rocket engines. The most feasible method of closing out channels with these alloys is by plasma spraying. Plasma spraying involves deposition of the molten metal and requires heating the substrate to within several hundred degrees of the melting temperature of the deposited metal. The channel filler material thus must be able to withstand the high deposition temperature without melting and must also be able to be stripped from the closed out channels without damaging the part.
Stripping without damaging the part is a difficult requirement because most elevated temperature materials are chemically very stable and require very strong concentrated acids or molten salts to dissolve if they can be dissolved at all. These high temperature material solvents also dissolve virtually all metals used in hardware construction. The present invention describes a high temperature material that can withstand the plasma spray processes without reacting with the deposited alloys and can be dissolved after spraying without damaging the plasma sprayed part.